Process of treating rubber and products obtained thereby



No Drawing. Original application filed March 2, 1928, Serial No. 258,670. Divided and this application filed. March 2, 1928.

Patented Apr. 21, 1931 UNITED STATES PATENT OFFICE SIDNEY M. CADWELL, O LEONIA, NEVT JERSEY, ASSIGNOR TO THE NAUG-ATUCK CHEMICAL COMPANY, OF NAUGATUCK, CONNECTICUT, A CORPORATION OF CON- NECTICUT PROCESS OF TREATING RUBBER ANDPRODUCTS OBTAINED THEREBY' particularly concerned with new classes of "1 chemical compounds capable of functioning as accelerators of vulcanization.

This case is a division of copending application Serial No. 258,670, filed of even date.

Accordingly the objects of the invention include the vulcanization of rubber treated with the hereinafter described classes of compounds. Another object is to provide new chemical compounds, particularly useful. in the vulcanization, which are comparatively inexpensive and at the same time highly efficient both from the standpoint of their behavior during the compounding of rubber as well as in the properties which they impart to the vulcanized product. Another object of the invention is to accelerate the action of the new chemical compounds by the addition of base or to retard their action by the addition of acid material. A further object of the invention is to provide a method whereby the acid or base or the new compounds themselves may be introduced into rubber.

In the present practice of the use of accelerators, it is generally known that many of the compounds employed are so powerful that they cause aprevulcanization, or burning on the mixing mill. This serious disadvantage is possessed by many of the accelerators which have the property of vulcanizing rubber at ordinary temperatures or attemperatures ,well below those ordinarily employed in hot vulcanization, for example at 212 F. or thereabouts. Illustrations of such rapid acceleratorsare metallic dithiocarbamates, metallic salts of other thioacids, mercapto thiazoles and the like. According to the present invention this serious objection of prevulcanization may be entirely overcome, the rubber compounds may be mixed upon the'mill with practically no danger of prevulcanization thereon, without sacrificing Serial No. 258,678.

and similar vulcanizable .materials with a Vulcanizing combination, including a vulcanizing agent, a metallic oxide or its equivalent and an S-triphenylmethyl derivative of a substituted dithiocarbamate, and vulcanizing the rubber. This invention has also been set forth in copending application Serial No. 258,670, filed of even date. The invention includes the products thus obtained and the preparation of the chemicals themselves. The new compounds may be prepared by the same general procedure as set forth in copcndin application Serial No. 258,670, that is, by the reaction of a sodium salt of the substituted dithiocarbamic acid and a triphenyl chlor methane.

he invention further consists in accelerating the action of the compounds by the ad dition of basic materials and in retarding the action of the compounds and particularly the burning of the compounds by the addition of acid materials. The invention further consists in introducing basicmaterials or acid materials or the compounds herein disclosed by diffusion from rubber or from any surrounding medium.

The whole compound, for example, triphenyl methyl diethyl dithiocarbamate (M. P. 150-155 G), reacts at least as rapidly with sodium hydroxide in boiling aqueous alcohol as diphenylmethyl dimethyl dithiocarbamate reacts under the same conditions. All the compounds which react with sodium hydroxide at least as rapidlyas diphenylmethyl dimethyl dithiocarbamate, accelerate vulcanization, in the presence of a metallic oxide, such as zinc oxide or an equivalent metallic compound. Those compounds which do not hydrolyze at such a rate do not accelerate vulcanization.

Zinc oxide is a good illustration of a metallic oxide which may be used. in place of zinc the following elements may be used in combined form, preferably somewhat basic and soluble in rubber; mercury preferably in the mercuric state, lead preferably in the plumbeous state, cadmium, copper preferably in the cupric state, arsenic preferably in the arsenious state, manganese preferably in the manganous states. Preferably the metallic compound is of such a nature that the metallic element is available during the vulcanization process. Oxides, stearates, carbonates are among the metallic compounds which may be used.

As one illustration of the invention, 100 parts of pale crepe, 10 parts of zinc oxide, 3 parts of sulphur, and 0.4 part of triphenyl methyl diethyl dithiocarbamate may be mixed together in the customary Way on a mixing: mill or in any other desired inanncr. T he rubber stock thus prepared is well vulcanized in minutes at 10 lbs. steam pressure. The stock niay also be vulcanized at higher steam pressures than 10 lbs.

Triphenyl methyl diethyl dithiocarbamate functions well when the cure is carried out according to any of the commercial inetl'iods, such as in steam, talc, water, etc. Other diallryl dithiocarbamates may be employed. pro vided they specify the conditions of hydrolysis herein set forth.

I have observed that the action of the compounds disclosed herein is accelerated by he presence of a small amount of a basic material such as sodium hydroxide, trisodium phosphate, dicyandiamide, pipcridine. aniline, dibenzylamine, piperazine hydrate, tricthauolamine. The use of the base lowers the temperature at which the accelerator functions or increases its speed of funct onii and usually increases the tensile strength at all temperatures of vulcanization by about 10%.

The base may be employed in aiuounts Q91: erally less than 1% or thereabouts.

Since a basic substance accelerates t to ac tion of the accelerator and lowers the tem perature at which it functions, it also increases the speed of burning on the mixing Therefore the greater the amount of b c present in the mix, the greater the danger 1e mixin r mill and rubbers ne therettore accelerate the E compounds. Burning; on the {ne form of what is herein The latter tion operation. This is particularly true of the dinitrophenyl compounds.

On the other hand the addition of acid retards the action of the accelerator and the efore increases its resistance to burning.

For example .1 part of monochlor acetic acid added to the above stock minimizes any danger of burning on the mill, but at the same time does retard the rate of vulcanization. With larger amounts of acid it is possil le to r tard vulcanization almost to the point where no vulcanization takes place. Other acids which I have successfully employed'are sulphanilic, oxalic, picric, phosphoric, trichloracetic, )ara toluene sulphonyl chloride and pine tar. I have also successfully employed substances which may form acids during the course of vulcanization such as ethyl oxalate, or zinc acetate.

Mixes which are slightly acid because of the presence of carbon black or pine tar resist burning on the mill abnormally Well.

The vulcanization of rubber which are acid by nature, or contain appreciable amounts of acid or acidic ingredients, is not accelerated so well by the herein described compounds, unless the acidic properties be first removed or neutralized.

Likewise, rubbers or rubber stocks Which are appreciably basic by nature, or contain basic materials, may display a marked, often undesirable tendency towards prevulcanization. Such basic rubbers or stocks ma be treated with acidic material. to remove, to curb, or to control this tendency to prevulcanize. Therefore, by the use of basic material and acidic material in suitable proportions as required. any rubber or stock may be brought to a predetermined speed of vulcanization.

Instead of adding on the mixing roll the basic materials intended to activate the compounds or accelerate their action, one may permit the basic material to diffuse into the rubber. For instance if the stock given above for vulcanization in the air be vulcanized in air containing ammonia, the vulcanization is greatly accelerated and the surface of the stock is remarkably hard and resistant to mar-ring. The introduction of the basic material may be made on the mill by diffusion from. a liquid, solution, or gas, or from adjoining rubber stock or from a fabric.

For example a. stock containing 100 parts of pale crepe, 10 parts of zinc oxide. 3 parts of sulphur and 0. L part of triphenyl methyl diethyl dithiocarhamate, made up in the usual manner, may be sheeted to say .060 inches thickness or may be in the form of an article. If the sheet or article be treated with gaseous ammonia for about 16 hrs, it will vulcanize very much more rapidly and at a lower temperature than a stock not so treated. Instead of gaseous ammonia, I may employ aqueous ammonia, aqueous diethyldiethyl dithiocarbamate.

calendered to a thickness of .010.

amine, aqueous aniline or dime'thyl'amine or aniline vapor. It is believed that these basic materials diffuse into the rubber and accelerate the action of the triphenyl methyl As an example of the introduction by diffusion of-the basic material as well as the introduction by dilfusion of some of the compounds disclosed herein, the following illustration is given: 100 parts of pale crepe,

10 parts of zincoxide, 3 parts of sulphur, 1 part of triphenyl methyl diethyl dithiocarbamate and .2 part of monochlor acetic acid are mixed to form one stock which is Another stock is made up of 100 parts of pale crepe, 10 parts of zinc oxide, 3 parts of sulphur and 4 parts of dibenzylamine. This stock is mixed on the mills in the usual manner and calendered to a thickness of .010". The two stocks are plied up alternately using 3 plies of each and allowed to stand for 24 hours to permit the diffusion of the dibenzylamine into the triphenylmethyl stock and of the triphenylmethyl diethyl dithiocarbamate into the dibenzylamine stock. Thereafter the plied up stock is heated at 212 and it is found that vulcanization occurs much more quickly than it does for the individual stocks which have not been plied up: It will be ob served that the dibenzylamine acts to neutralize the monochlor acetic acid as well as to activate the triphenyl methyl diethyl ditriocarbamate.

As pointed out before the presence of the monochlor acetic acid improved the resistance to burning but the procedure may be carried out without the use of the acid.

The basic material (ammonia, etc.) may be introduced from the surrounding medium such as air or water to neutralize the acids and/or to activate the accelerator. For instance if .2 part of acid be added to the stock for air cure given above, and the stock be curedin air containing ammonia gas, the

ammonia will not only neutralize the acid but will activate the triphenyl methyl compound, The basic material may be introduced in any desired manner at any time prior to complete vulcanization, i. c. it may be introduced during vulcanization as a gas or vapor, or it may be applied to the stock by painting, dipping, or blending in cement form, etc. before the stock is subjected to vulcanization, or the stock may be vulcanized in a solution or suspension of the basic material.

Any of these ingredients, base, acid, and

accelerator may be brought together in the form of cements, i. e. a cement containing accelerator may be mixed with a cement containing the base at the time the cement 1s to be used. The accelerator cement will not vulcanize appreciably at ordinary temperatures if the base be absent. Likewise, an ac- "celerator-containing cement may be prezation is desired, a base may beladded as (such, in solution, or in acement) and vulcanizatlon Wlll then take place.

The accelerating compounds in general may be used 111 amounts varying between i to 2 parts in 100 parts of rubber, depending ofcourse on the type of stock, etc.

All of the above mentioned compounds are accelerators of vulcanization. Some of them give high tensile strength and other valuable physical properties such as improved resistance to abrasion, ageing, and other properties. The claims are therefore to be broadly interpreted as including such treatment of rubber in any form (solid, solution, dispersion) for these purposes as well as for vulcanization, in which latter instance, 'it isunderstood that a vulcanizing agent and a metallic oxide or its equivalent will be added to the rubber and an antioxidant or other material improving the physical properties of the rubber may be present'if desired. It is of course understood that not all of these compounds are of 7 equal accelerating strength, pound for pound, under identical vulcanizing conditions. These accelerators may be used in conjunction with any-of the known anti-oxidants, age improvers, and other materials introduced into rubber to improve ageing and other physical properties.

It is believed that, in general, as the molecular weight of the groups attached to the nitrogen'is increased the higher is the vul canizing temperature, when equi-molecular amounts of accelerator are considered, and the more resistant are the compounds to pre-vulcanization on the mixing mills, and the better is their action with litharge in the absence or presence of zinc oxide. 7

The rate of reaction of the compound with sodium hydroxide in boiling aqueous alcohol may be determined as follows:

001% moles of the'compound is Weighed into a 50 cc. Erlenmeyer; 25 cc. 95% alcohol and .00125 moles sodium hydroxide in the form of an approximately normal solution are added and the solution brought to the boiling point as quickly as possible and kept there for exactly 30 minutes. The solution is then cooled quickly and titrated with approximately h /10 acid, using phenolphthalein as the indicator. Carbon dioxide-free water should be used throughout. A blank should be run in order to check up on the amount of acid necessary to neutralize the so- .dium hydroxide when no compound is used. The, decrease in hydroxyl ion content during the'boiling is taken as a measure of the any given compound of the types disclosed carbamate under may be compared with that of diphenylmethyl dimethyl dithiocarbamate.

The diphenylmethyl dimethyl dithiocarbamate may be prepared in accordance with the general procedure indicated herein, that is reacting a solution of a salt (preferably the sodium salt) of dimethyl (lltlllOCHlbfllIllC acid with diphenyl chloro-methane. Diphenylmethyl dimethyl dithiocarbama-te separates as an oil which solidifies and crystallizes on standing over night and may be purified by recrystallization from alcohol. It has a melting point of 96.5%)7" C.

It is known that the rate of hydrolysis of organic compounds, or more exactly, their rate of reaction with a base such as sodium hydroxide varies with the substituent in the organic compound. This variation has been utilized in the present invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

l. A rubber product derived from rubber combined with a metallic oxide, a vulcanizing agent and a triphenyl methyl ester of a substituted dithiocarbamic acid which ester is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least rapidly as diphenyl methyl dimethyl dithiocarbamate under the same conditions.

2. A vulcanized rubber product derived from rubber combined with a metallic oxide, a vulca-nizing agent and a triphenyl methyl ester of an alkyl dithiocarbamic acid which ester is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydroxide at least as rapidly as diphenyl methyl dithiocarbamate under the same conditions.

3. A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and a triphenyl methyl ester of a dialkyl dithiocarbamic acid.

A vulcanized rubber product derived from rubber combined with zinc oxide, sulphur and triphenyl methyl diethyl dithioearbamate 5. A method of treating rubber which comprises vulcanizing rubber containing a metallic oxide and a vulcanizing agent in the presence of a triphenyl methyl ester of a substituted dithiocarbamic acid which ester is capable of hydrolyzing in aqueous alcohol in the presence of sodium hydr at least as rapidly as diphcnyl methyl dime hyl dithiocarbatnate under the same conditi 1 3i '15 d of treating rubber nizing rubber contai tallic oxide and a Vulcanizing a presence ci a triphenyl met alkyl ditliiocarbamic acid w QotCl' of an A ester is capable of hydrolyzing n aqueous alcohol in the presence of sodium hydr ride at least as rapidly as diphenyl inc yl dimethyl dithio- 1 same conditions.

a. is method of treating rubber which com-- 

